1. Field of the Invention
This invention relates to an oscillator and a frequency synthesizer and a communication apparatus using the oscillator.
2. Description of the Prior Art
There are two types of oscillators for oscillating at a high frequency band such as a quasi-microwave band or the like, namely, the first type of oscillator directly oscillates at the desired frequency and the second type of oscillator oscillates at a low frequency and a frequency up-converter coupled to the oscillator provides an up-converted frequency output. The second type of oscillator is frequently used due to easiness in designing and a reduction of a consumed current. Frequency synthesizer and communication apparatus using such a prior art oscillator are also known.
Hereinafter, a prior art high frequency band oscillator will be described.
FIG. 20 is a block diagram of the prior art high frequency band oscillator.
In FIG. 20, numeral 1 denotes a ring resonator, numeral 2 denotes an oscillation portion comprising a negative resistance active circuit using transistors or the like, and numeral 3 denotes a coupling capacitance for coupling between the ring resonator 1 and the oscillation portion 2. Numeral 5 denotes a frequency up-converter comprising non-linear elements such as transistors, numeral 6 denotes a bandpass filter (BPF) for outputting an up-converted frequency output of the frequency up-converter and attenuating unnecessary waves, numeral 7 is an output terminal, and point A is a coupling point between the ring resonator 1 and oscillation portion 2.
An operation of the prior art high frequency band oscillator having the structure mentioned above will be described.
At first, the oscillator 4 oscillates at a frequency determined by an electrical length of the ring resonator 1 and a circuit constant of the oscillation portion 2. Because the frequency up-converter 5 comprises non-liner elements such as transistors and has a function generating a higher harmonic wave of the input signal, a double frequency output is obtained from the output of the oscillator 4 by the frequency up-converter 5. However, since an output level of a basic wave is generally larger than that of the double frequency output, it is necessary that a BPF 6 for attenuating the basic waves is connected at a rear stage of the frequency up-converter 5. Therefore, the double frequency waves can be obtained from the output terminal 7.
On the other hand, a frequency synthesizer comprising the rink resonator, and the oscillation portion and a phase synchronizing circuit is known. In such a phase synchronizing circuit, it is necessary to divide the output of the oscillator into a signal for an input of a phase synchronizing circuit and another signal for the external output.
Such a prior art frequency synthesizer will be described more specifically.
FIG. 21 is a block diagram of a prior art frequency synthesizer.
In FIG. 21, since elements denoted by numerals 1 to 4 and 7 and the point A are the same as FIG. 20, the detailed description is omitted. Numeral 8 denotes a distributor for outputting distribution outputs with a isolation degree therebetween kept, numeral 9 denotes a phase synchronizing portion having a frequency divider, a phase comparator, and a charge pump or the like, and numeral 10 denotes a loop filter for feeding back an output of the phase synchronizing portion 9 with high frequency components removed. Numeral 11 is a reference signal generator, and numeral 12 denotes a phase synchronizing circuit comprising the phase synchronizing portion 9, the loop filter 10, and the reference signal generator 11.
An operation of this prior art frequency synthesizer will be described.
The output of the distributor 8 is phase-compared by the phase synchronizing portion 9 with the reference signal from the reference signal generator 11. The phase synchronizing portion 9 supplies a synchronizing signal to the oscillation portion 2 through the loop filter 10 with unnecessary high frequency component removed wherein the outputs of the distributor 8 should have a sufficient isolation degree.
However, the prior art oscillator shown in FIG. 20 has problems that the circuit scale becomes larger and the 5 consumed current becomes large because the frequency-up converter and the prior art frequency synthesizer shown in FIG. 21 have problems that the circuit scale is large and the consumed current is large because the distributor are necessary in addition to the oscillator.